When video is streamed over the Internet and played back through a Web browser or media player, the video is delivered in digital form. Digital video is also used when video is delivered through many broadcast services, satellite services and cable television services. Real-time videoconferencing often uses digital video, and digital video is used during video capture with most smartphones, Web cameras and other video capture devices.
For standard dynamic range (“SDR”), digital video represents common colors in a relatively narrow range of brightness. Brightness can be measured in candelas per square meter (cd/m2), which indicates luminous intensity per unit area. This unit of luminous intensity per unit area is called a “nit.” A typical SDR display device may represent colors from pale colors through colors that are relatively vivid, in a brightness range from 0 nits to 100 nits. More recently, display devices having high dynamic range (“HDR”) have been introduced. A typical HDR display device may represent colors in a wider color gamut (potentially representing colors that are more vivid or saturated) and in a larger brightness range (e.g., up to 1500 nits or 4000 nits). Video produced for playback on an HDR display device can have an even larger brightness range (e.g., 0 nits to 10,000 nits).
When HDR video content is played back on an SDR display device, details in moderately bright values and very bright values are lost. For example, brightness values above a certain threshold (e.g., 100 nits) are clipped to the brightest value possible for the SDR display device, or brightness values above a certain threshold (e.g., 95 nits) are compressed to a very small range, so that a very wide range of bright values in the HDR video is represented with a small range of values on the SDR display device. Recently, some display devices have an enhanced dynamic range (“EDR”) that, compared to a typical SDR display device, supports a larger range of brightness values (e.g., up to 400 nits or 600 nits). The increase in range of brightness values can be called “brightness headroom.” To date, the brightness headroom of EDR display devices is not exploited efficiently when rendering HDR video.